Synthesis of co-doped high voltage lithium cobalt oxide with high rate electrochemical performance

Abstract

LiCoO2 can further develops its capacity potential by increasing cut-off voltage, but the irreversible phase transition and structural damage at high voltage will lead to severe capacity fading. Here, we propose a method of multi-doping of four elements Ti, Mg, Al, and Y, which realizes the stable cycling of LiCoO2 at a cut-off voltage of 4.5 V through the synergistic effect among the four elements. The cell delivers the increased initial discharge capacity of 173.5 mAh/g, with the capacity retention rate as high as 91.1% after 100 charging-discharging cycles at the rate of 1 C in the voltage ranging from 3.0 to 4.5 V. Moreover, the capacity retention is still as high as 74.2% after 300 cycles. At the same time, the capacity can still be maintained close to 70% after 100 cycles at the temperature of 50 ℃. The specific discharge capacity of the cathode is 130.0 mAh/g, even if at high rate of 5 C. More than 5 times that of unmodified LiCoO2. We verified the effect of four-element co-doping on phase and surface stability by characterizing the materials before and after the cycle. At the same time, the positive effects of four doping elements on structural stability and electronic conductivity were clarified by DFT method. This work provides a promising idea of multi-element synergistic doping and contributes to solving problem of stable high voltage LiCoO2.